In recent years, with improvements in technology and efficiency, ultraviolet light emitting diodes (UV LEDs), with their longer lifespan and smaller volume, have been slowly replacing mercury lamps of lower efficiency. With the Minamata Convention on Mercury coming into effect in 2020, the global ban on mercury would further expedite the rise of application of the UV LEDs.
A conventional deep UV LED has an aluminum nitride (AlN)-based buffer layer. FIG. 1 shows an epitaxial structure of the conventional deep UV LED. An n-type nitride semiconductor layer 130, a quantum well light emitting layer 140 and a p-type nitride semiconductor layer 150 are formed sequentially on the AlN-based buffer layer 120 grown on a substrate 110. In particular, because there is lattice mismatch between the n-type nitride semiconductor layer and the AlN-based buffer layer, high compressive stress is experienced by the latter-grown aluminum gallium nitride (AlGaN)-based layers such as the quantum well light emitting layer and the p-type nitride semiconductor layer. This causes an increase in the dislocation density and affects the lattice quality as well as the luminous efficiency of the deep UV LED.